Fixing device and image forming apparatus

Abstract

A fixing device includes a nip formation pad to form a fixing nip between a first fixing rotator and a second fixing rotator, through which a recording medium bearing a toner image is conveyed. The nip formation pad includes a first planar face, a second planar face disposed downstream from the first planar face in a recording medium conveyance direction and being parallel to the first planar face, and a joint face bridging the first planar face and the second planar face. The joint face includes a first curved portion adjoining the first planar face and having a first curvature in a first direction in which a circumferential face of the second fixing rotator is curved and a second curved portion adjoining the second planar face and having a second curvature in a second direction opposite the first direction.

What is claimed is: 
     
       1. A fixing device comprising:
 a flexible, first fixing rotator rotatable in a predetermined direction of rotation; 
 a second fixing rotator disposed opposite the first fixing rotator and including an elastic layer; 
 a heater to heat one of the first fixing rotator and the second fixing rotator; and 
 a nip formation pad to press against the second fixing rotator via the first fixing rotator to form a fixing nip between the first fixing rotator and the second fixing rotator, the fixing nip through which a recording medium bearing a toner image is conveyed, 
 the nip formation pad including:
 a first planar face; 
 a second planar face disposed downstream from the first planar face in a recording medium conveyance direction, being parallel to the first planar face, and having a length shorter than a length of the first planar face in the recording medium conveyance direction; and 
 a joint face bridging the first planar face and the second planar face, the joint face including: 
 a first curved portion adjoining the first planar face and having a first curvature in a first direction in which a circumferential face of the second fixing rotator is curved; and 
 a second curved portion adjoining the second planar face and having a second curvature in a second direction opposite the first direction. 
 
 
     
     
       2. The fixing device according to  claim 1 , wherein the first planar face, the joint face, and the second planar face are arranged in the recording medium conveyance direction to define the fixing nip. 
     
     
       3. The fixing device according to  claim 1 , wherein the first curvature of the first curved portion is greater than a third curvature of the circumferential face of the second fixing rotator. 
     
     
       4. The fixing device according to  claim 1 , wherein the first planar face adjoins the first curved portion to share a first common tangent and the second planar face adjoins the second curved portion to share a second common tangent. 
     
     
       5. The fixing device according to  claim 1 , wherein the first curved portion adjoins the second curved portion to share a third common tangent. 
     
     
       6. The fixing device according to  claim 1 , wherein each of the first curved portion and the second curved portion defines a cylindrical surface. 
     
     
       7. The fixing device according to  claim 1 , wherein the first planar face defines an entry to the fixing nip through which the recording medium enters the fixing nip. 
     
     
       8. The fixing device according to  claim 1 , wherein the second planar face defines an exit of the fixing nip through which the recording medium is ejected from the fixing nip. 
     
     
       9. The fixing device according to  claim 1 , wherein the second curved portion is disposed downstream from a rotation axis of the second fixing rotator in the recording medium conveyance direction to increase a compression rate of the elastic layer of the second fixing rotator. 
     
     
       10. The fixing device according to  claim 1 , wherein the first curved portion is curved along the circumferential face of the second fixing rotator. 
     
     
       11. The fixing device according to  claim 1 , wherein the first curved portion is recessed relative to the circumferential face of the second fixing rotator and the second curved portion projects toward the circumferential face of the second fixing rotator. 
     
     
       12. The fixing device according to  claim 1 , wherein the nip formation pad further includes a guide face adjoining and being disposed downstream from the second planar face in the recording medium conveyance direction, the guide face to direct the recording medium toward the second fixing rotator. 
     
     
       13. The fixing device according to  claim 12 , wherein the guide face is recessed relative to the second fixing rotator. 
     
     
       14. The fixing device according to  claim 12 , wherein the guide face is planar to share an identical plane with the second planar face. 
     
     
       15. The fixing device according to  claim 1 , wherein the first planar face and the second planar face are aligned along a direction substantially perpendicular to a hypothetical line defined by a rotation axis of the first fixing rotator and a rotation axis of the second fixing rotator. 
     
     
       16. The fixing device according to  claim 15 ,
 wherein the rotation axis of the second fixing rotator and the first planar face of the nip formation pad define a line that is perpendicular to the first planar face at an intersection, and 
 wherein the second curved portion is downstream from the intersection in the recording medium conveyance direction. 
 
     
     
       17. The fixing device according to  claim 1 , wherein the nip formation pad further includes a round portion disposed downstream from the second planar face in the recording medium conveyance direction, the round portion having an increased curvature to bend the first fixing rotator in a direction in which the first fixing rotator separates from the second fixing rotator. 
     
     
       18. The fixing device according to  claim 1 , wherein the first fixing rotator includes an endless belt and the second fixing rotator includes a roller. 
     
     
       19. The fixing device according to  claim 1 , wherein the length of the first planar face is longer than a length of the first curved portion in the recording medium conveyance direction. 
     
     
       20. An image forming apparatus comprising:
 an image forming device to form a toner image; and 
 a fixing device disposed downstream from the image forming device in a recording medium conveyance direction to fix the toner image on a recording medium, 
 the fixing device including:
 a flexible, first fixing rotator rotatable in a predetermined direction of rotation; 
 a second fixing rotator disposed opposite the first fixing rotator and including an elastic layer; 
 a heater to heat one of the first fixing rotator and the second fixing rotator; and 
 a nip formation pad to press against the second fixing rotator via the first fixing rotator to form a fixing nip between the first fixing rotator and the second fixing rotator, the fixing nip through which the recording medium bearing the toner image is conveyed, 
 
 the nip formation pad including:
 a first planar face; 
 a second planar face disposed downstream from the first planar face in the recording medium conveyance direction, being parallel to the first planar face, and having a length shorter than a length of the first planar face in the recording medium conveyance direction; and 
 a joint face bridging the first planar face and the second planar face, 
 
 the joint face including:
 a first curved portion adjoining the first planar face and having a first curvature in a first direction in which a circumferential face of the second fixing rotator is curved; and 
 a second curved portion adjoining the second planar face and having a second curvature in a second direction opposite the first direction.